I. Technical Field
This invention relates to construction of prefabricated building modules and more particularly to bonding structural reinforcement members to flexible panels.
II. Brief Description of the Background Art
In the manufacture of prefabricated homes or mobile homes, it is preferred to bond wooden trusses or studs to flexible gypsum or fiber board panels with a polyurethane foam adhesive, according to the technique disclosed in my prior U.S. Pat. No. 4,244,901. When wood supports are laid upon the flat surface of the gypsum or fiberboard substrate, gaps are formed between the wood and the substrate. Polyurethane foam adhesive flows into and expands in the gaps formed between the structural member and the substrate. The bond between the structural member and the panel provides good support for the panel without mechanical fasteners, and provides a flat, continuous surface which compensates for and actually benefits from any inherent warpage in the structural support members.
Metal support members currently being considered for use in building modules are generally formed with substantially smooth and flat walls that fit flush against the substrate. Metal support members are non-porous and may have lower adhesion than wood support members or the panels to polyurethane foam adhesives. Minimal gaps are formed between the support and the substrate into which the liquid polyurethane resin can flow and expand. When a stream of liquid polyurethane thermosetting resin is directed at an angle under pressure at the juncture between the structural elements and the panel, the resin forms a fillet, or convexly curved section, at the angle formed by the junction of the panel and the support member. Stresses tending to separate the panel from the support member are primarily resisted by the shear strength of the adhesive bond to the perpendicular surface of the support member. With wooden support members, separation is resisted by both the tensile strength of the urethane as it is bonded to opposed facing surfaces of the panel and the support member and the shear strength of the adhesive bond to the perpendicular surface of the support member.
Another problem presented by the use of metal support members is that the thermal conductivity of the metal support members results in the transfer of heat energy. With wooden support members, the inherent insulative properties of wood reduce the transfer of heat through the support members. Structural panels are generally insulated between support members, but heat can be transferred through the support members if they are formed of metal.
It is an object of the present invention to improve the adherence of rigid metal or support members to a substrate such as gypsum wall board or fiber board.
Another object of the present invention is to establish a predetermined space between support members and substrates which may be filled with a liquid polyurethane resin wherein forces tending to separate the support members from the substrates are opposed by the tensile strength of the polyurethane resin bond. Also, by filling the space, the surface area available for bonding between the resin, support members and panel is increased.
A further object of the present invention is to establish a thermal break between substrates and metal support members, such as steel and aluminum support members.
In addtion to the increased surface area for bonding and reliance upon tensile strength of the polyurethane resin, it is an object to further improve the bonding between the substrate and support member by providing a mechanical interlock of polyurethane resin and the support members. Portions of the support members include holes or are specially formed to create the mechanical interlock when the polyurethane resin expands through and bonds to the specially-formed portions.